The emission of sulfur dioxide (SO2) from sulfur bearing fuels has been recognized as an environmental problem for many decades. Regulations have been implemented to attempt to reduce the emission of SO2. It is known that SO2 is a major air pollutant and has significant impacts upon human and animal health. In addition high concentrations of SO2 in the atmosphere can influence the habitat suitability for plant communities. Further, SO2 emissions are a precursor to acid rain and atmospheric particulates.
Historically, burning coal and fuel oil used in power boilers resulted in a high level release of SO2. In recent years, petroleum coke has become an alternative fuel. Petroleum coke (a waste product from crude oil) is typically derived from coking heavy oil at many oil refineries. Petroleum coke has high sulfur content which when burned has high SO2 emissions. If the crude oil is sour, the resulting coke will have high sulfur content.
Approximately over 50% of the current U.S. power supply comes from coal fired power plants. The fuel is selected on a balance of BTU value and sulfur content. All new plants built since 2005 must conform to stringent SO2 emission controls. The consequence is the necessity to install fuel gas desulfurization (FGD) systems. These desulfurization systems are methods of contacting the flue gas laden SO2 with alkali sorbents. The alkali sorbents may be limestone, lime and sodium base alkali. The sorbents can be applied as slurries or dry powders. In some uses, the flue gas is placed in contact with the sorbents to achieve the longest contact and at the temperature most favorable to the alkali to acid reaction. The most favorable temperature range is frequently estimated as 750 C to 1100 C. The most efficient capture of SO2 is stated to be in a range of 900 C to 1100 C. There has been much experimentation in determining the effect of the surface area of the alkalis with efficiency of SO2 capture. The high temperatures needed to ensure capture result in loss of generation capacity and/or increased energy consumption.
The costs of attempting to capture the SO2 with current systems are high. For example, the capital, operating and maintenance cost per short ton of SO2 removed (in 2001 US dollars) are highest for wet scrubbers (largest percentage of FGD scrubbers). For wet scrubbers larger than 400 MW, the cost is $200 to $500 per ton. For wet scrubbers smaller than 400 MW, the cost is $500 to $5,000 per ton. Similarly with spray dry scrubbers larger than 200 MW, the cost is $150 to $300 per ton and for spray dry scrubbers smaller than 200 MW, the cost is $500 to $4000 per ton.
For small boilers, such as hog fuel boilers, the capital cost and maintenance of these wet scrubber systems are prohibitive. Injecting sorbent into flue gas passing through spray towers or contact beds have plugging problems that are inherent to the system.
Due to the high costs of remediation, another option that is currently used is to transport the high-sulfur fuel to a waste destination where regulations may be less stringent. However, although it may be possible to ship the high sulfur fuel (waste product) to a waste destination, the burning at the waste destination results in a release of SO2 (although in a different location). Moreover, waste product which is simply stored has further negative environmental effects. Likewise, transport impacts in moving the waste fuel, including rail and shipping impacts, have negative environmental effects.
The inventors herein have recognized the above-mentioned disadvantages and have developed apparatus and methods for producing a manufactured fuel pellet made from high sulfur carbonaceous compounds which emits a reduced level of SO2 upon burning. In some example embodiments, petroleum coke is included in a fuel composition that utilizes the high carbon content of the coke, a biomass constituent that provides the volatiles to make the volatile deficient coke more ignitable and an alkali constituent to capture the SO2 produced by burning high sulfur coke. In other examples, a catalyst, such as an iron oxide catalyst may further be added to increase the capture of SO2. The fuel composition may be formed as pellets, powders, briquettes, beads or any other agglomerates.
The present embodiments disclosed herein may provide several advantages. Specifically, the approach may reduce the level of released SO2. In addition, the approach utilizes waste materials which previously required storage, transportation or alternative processing. By providing the herein disclosed high sulfur fuel pellet with reduced SO2 emissions, environmental impact of the waste product can be reduced while still utilizing the fuel properties of the product.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.